dbdma: update xferStatus and resCount when handling FLUSH command

[mihaip]

Per the DBDMA spec (section 15.4.3), this is required:

ChannelStatus.flush can be set to 1 by software, to force a channel that is executing an INPUT_MORE or INPUT_LAST command to update memory with any data that has been received from the device but has not yet been written to memory. When the memory update is complete, hardware updates the xferStatus and resCount fields in the current memory resident channel command, then clears the flush bit. Thus, a partial status update is characterized by 1 in the flush bit of the xferStatus field and a final status update is characterized by 0.

Fixes a hang when booting 9.0 and 9.0.4 on the Beige G3 (they would get stuck in a loop polling the xferStatus.active field).